Weighting scales capable of rapidly weighing a series of flat articles have recently been developed. One type of such scale is a vibrating tray scale wherein a flat article is conveyed onto the platform of the scale, the conveying mechanism is removed from contact with the article, a holding device holds the flat article firmly on the platform, and the platform is oscillated thereby causing flex-members that support the platform to oscillate. A transducer is attached to one of the flex-members to measure the frequency of oscillation of the platform. Based upon such measurement, the weight of the article on the platform can be determined. Details relative to the structure of a vibrating tray scale, the method of operation and the method of determining the mass of an article thereon are fully described in U.S. Pat. No. 4,778,018. With such a scale, one is able to weigh articles at rate of two to four articles per second. The rate of weighing depends upon the size of the articles to be weighed as well as the characteristics of the particular vibrating tray scale.
One of the important features of a vibrating tray scale is the need to lock the base of the scale when the tray is not being vibrated for purposes of obtaining the weight of an article on the tray. The base of the scale is that part which provides support to the flex-members and the base in turn is supported by a frame or housing. Various locking mechanisms have been used with success for the purpose of achieving stabilization of the base during the time articles are transported on and off the tray. In U.S. Pat. No. 4,778,018 a solenoid type of device is used that clamps onto the base from the top and bottom. In U.S. Pat. No. 4,836,311 a mechanism is described that not only provides a locking mechanism but also initiates the oscillation of the tray. In U.S. Pat. No. 4,844,188 a mechanical locking device is shown that is activated to lock the base upon the article transporting mechanism being activated and deactivated when the article is to be weighed. Although all of these locking mechanisms have worked satisfactorily well, a need still exists for a relatively simple, reliable and fast locking mechanism.